Acute venous thrombosis (also referred to as acute deep venous thrombosis (DVT)) is a condition where blood clots (thrombosis) form inside veins. An acute clot is initially soft (jelly-like). The vessel and surrounding tissue will respond with an inflammatory reaction and over weeks and months the clot will become “hardened” and retract and partially obstruct the lumen. Classic symptoms of acute venous thrombosis include pain, swelling and redness of the leg and dilation of the surface veins. However, these symptoms may be absent in certain cases. The traditional treatment for venous thrombosis, in its early jelly-like stage, is to use blood thinners (anticoagulation) without removing the clot itself (anticoagulants often do not actively dissolve the clot, but prevent new clots from forming).
Removal of the thrombus in addition to anticoagulation is beneficial to long term patency. Currently, there are two main approaches to remove the clot in the early stage (generally, within 14 days of onset of symptoms): (1) dissolution or lysis of the clot by administering a clot dissolving enzyme (a lytic agent) through a catheter into the vein harboring the clot; or (2) removal of the clot by a mechanical device, sometimes priming the clot with a lytic agent prior to removal. In the “hardened” late stage (sometimes referred to as post-thrombotic disease), thrombectomy is generally ineffective, and the condition is generally treated with balloon angioplasty and possible stenting.
Currently available mechanical devices include the AngioJet (Possis Medical, Inc., Minneapolis) and the Trellis, manufactured by Bacchus Vascular, Inc., Santa Clara, Calif.
The AngioJet is a dual lumen catheter designed to rapidly remove blood clots with minimal vascular trauma. The AngioJet System is typically used in conjunction with thrombolytics. The Trellis is a drug infusion device designed for isolated thrombolysis. A thrombus is isolated between two occlusion balloons while the thrombolytic is mechanically dispersed with an oscillating wire and then aspirated.
Currently available mechanical thrombectomy devices perform poorly without lytic agents as their mechanical efficiency is poor. However, use of lytic agents poses the risk of inducing bleeding into normal tissues leading to serious complications such as stroke. Additionally, mechanical removal of clots presents the potential for embolism when portions of a clot break off and migrate to undesired locations. A new mechanical design is intended to improve clot removing efficiency without the need to employ a lytic agent and to reduce the occurrence of embolism.